Blood Service and Organ Donation

Community Medicine — Blood Service and Organ Donation, NMC MBBS licence examination syllabus (Nepal Medical Council).

The Blood Service and Organ Donation

A transfusion is the only treatment that requires another human being to have given part of themselves first.

Every unit of blood hanging on a drip stand started with someone who walked into a centre, answered a series of personal questions honestly, and gave an hour of their time for nothing.

That fact shapes the whole subject. The safety of the blood supply depends less on laboratory technology than on who donates and why — and the commonest fatal transfusion error happens not in the laboratory but at the bedside, with a checking step that takes thirty seconds.

ABO: learn the rule, not the table

Students memorise the compatibility table and then forget it. The table is unnecessary, because one rule generates all of it:

You carry antibodies against the ABO antigens you lack, and — unlike most antibodies — they are present from infancy without any prior exposure. So group A has anti-B, group B has anti-A, group O has both, and group AB has neither.

From that single fact everything follows. The question in any transfusion is never "what antigens does this blood have?" but "what will the recipient's antibodies attack?"

Group O red cells carry neither A nor B antigen, so no recipient's antibodies can attack them — hence universal red cell donor. But a group O person has both antibodies, so they can receive only O.
Group AB is the mirror image: no antibodies, so any red cells are acceptable — universal recipient. But AB cells carry both antigens, so they can be given only to AB.

💡 Exam angle, and a genuine trap: plasma runs the opposite way. Plasma carries the antibodies rather than the cells, so AB is the universal plasma donor (its plasma has no anti-A or anti-B) and O is the universal red cell donor. Candidates who memorised "O is universal donor" without the reasoning get the plasma question wrong every time. Work it out from the rule instead.

RhD, and why it dominates obstetrics

The D antigen behaves differently from A and B in one decisive way: anti-D is not present from birth. It is only produced after a D-negative person is exposed to D-positive red cells.

That has a specific and important obstetric consequence:

A D-negative woman carrying a D-positive fetus is usually not sensitised during that pregnancy.
At delivery, fetal cells enter her circulation and she may produce anti-D.
In a later pregnancy with a D-positive fetus, that anti-D crosses the placenta and destroys fetal red cells — haemolytic disease of the newborn.

So the first pregnancy is usually fine and the danger is to subsequent ones, which is exactly the pattern that makes prevention possible: anti-D prophylaxis given after a potentially sensitising event prevents the antibody forming at all. This is why a blood group is checked at antenatal booking on every woman.

The transfusion consequence follows directly: never give D-positive blood to a D-negative girl or woman of childbearing age unless there is no alternative in a life-threatening emergency. Sensitising her costs nothing today and may cost a future baby.

Where safe blood comes from

There are three ways to obtain blood, and they do not produce equally safe supplies.

Voluntary, unpaid, repeat donors give the safest blood. The reason is straightforward: someone donating altruistically has no reason to conceal a risk factor when the screening questionnaire asks about it. A repeat donor has also been tested before.

Paid donors produce measurably less safe blood, because payment creates an incentive to answer the screening questions in whatever way secures the donation. Replacement donation — where a patient's family must find donors before blood is issued — sits uncomfortably between the two, since it applies social pressure to people who may feel unable to decline or to disclose.

Why does donor selection still matter when every unit is tested? Because of the window period. A recently infected donor is infectious but has not yet developed detectable markers, so screening returns a negative result on genuinely infectious blood. Testing catches most of what selection misses — but not all of it, and the two are complementary rather than alternatives.

Every unit is screened for HIV, hepatitis B, hepatitis C and syphilis, with additional tests according to national policy. The exact panel and the assays used are set nationally.

The check that actually prevents deaths

This is the most practically important paragraph in the chapter.

The laboratory very rarely issues incompatible blood. Fatal haemolytic reactions are overwhelmingly identification errors: a sample labelled with the wrong patient's details, or a correctly labelled unit given to the wrong patient. Both happen at the bedside, and both happen when someone is busy.

So the safeguards are procedural, not technical:

Label the sample at the bedside, from the patient's own wristband, immediately after taking it — never in advance, and never at the desk afterwards.
Ask conscious patients to state their own name and date of birth rather than asking "are you Mr Sharma?", which a confused or deaf patient will agree to.
Perform the final check at the patient's side, matching the unit to the wristband, every single time — including for the second and third units.

The immediate management of a suspected acute transfusion reaction — stopping the transfusion first — is covered in the fluids and transfusion chapter.

Using blood well

Two system-level points complete the picture, and both are examinable.

Blood is a scarce donated resource, not a tonic. Transfusing a stable patient with mild anaemia exposes them to risk for no benefit and consumes a unit someone else needed. Where anaemia has a treatable cause — iron deficiency above all — treating the cause is better medicine than transfusing.

Component therapy replaces what is missing. Whole blood is separated so that one donation can treat several patients, each receiving the component they actually need — red cells, platelets or plasma — rather than everyone receiving everything.

Organ donation

Organ donation raises one structural principle that matters more than any clinical detail:

The diagnosis of death and the question of donation are entirely separate, and are handled by different people. Death is determined by clinicians with no involvement in transplantation, on purely clinical grounds. Only afterwards is donation raised. That separation is what makes the system trustworthy — and any blurring of it, however well intentioned, damages public confidence in a way that costs lives later.

Brain death is death, not a deep coma and not a prediction about the future. It means irreversible loss of brain-stem function — the patient will never breathe again unaided and will never regain consciousness. The heart may continue to beat while a ventilator supplies oxygen, which is precisely why the concept is difficult for families: the person looks asleep and feels warm.

Explaining that takes time and plain language. A family that has not understood that their relative has died cannot meaningfully consent to anything.

The specific tests required to diagnose brain death, who may perform them and how many examinations are needed are laid down in law and differ between countries. They are not listed here, and should never be carried out from memory — use the formal protocol.

Consent follows national law, which may operate on an opt-in or opt-out basis, and typically involves the family regardless. Commercial dealing in organs is prohibited, and the reason is worth stating plainly: a market in organs extracts them from the poor for the benefit of the rich, and no consent obtained under financial desperation is genuinely free.

Putting it together

You have antibodies against the antigens you lack. That one rule generates the whole ABO table — and plasma compatibility runs opposite to red cells.
Anti-D is acquired, not innate, so the risk falls on later pregnancies — and prophylaxis prevents it.
Voluntary unpaid donation gives the safest blood, because the window period means testing alone is not enough.
Fatal transfusion reactions are identification errors. Check at the bedside, and have the patient say their own name.
Death is diagnosed independently of any donation question — and brain death is death, not a coma.

No transfusion thresholds, storage conditions, deferral intervals, window-period durations or brain-death testing protocols are quoted here: all are set by national policy or by formal legal procedure. Use the actual protocol.

Syllabus points

The ABO rule; why plasma runs the opposite way
Anti-D is acquired — the obstetric consequence
Never D-positive blood to a D-negative woman of childbearing age
Voluntary unpaid vs paid vs replacement donation
The window period and why screening is not enough
Bedside identification — the check that prevents deaths
Appropriate use and component therapy
Brain death, separation of decisions, and consent

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